Coupling transformer



Juy 26,

193s. H, T; MAN 2,125,119 COUPLING TRANSFORMER s sheets-sheet 1 FiledJune 2, 1936 Harold? Lyman S A tor-wey July 26, 19381. H. T. LYMANCOUPLING TRANSFORMER 5 Sheets-Sheet 2 Fiied June 2, i956 Inventar:

Patented July 26, 1938 UNITED STATES PTET OFFICE l 2,125,119 coUPLINGTRANsFoRMER York Application June 2, 1936, Serial No. 83,057

11 Claims.

My invention relates to coupling devices for electric circuits and moreparticularly to coupling units which are adapted to be used in couplingsuccessive stages of an electron discharge ampliy, er system.

The advantages of transformer coupling in high frequency electriccircuits over other forms of coupling are well known. This type ofcoupling is particularly advantageous in connection with electrondischarge amplifiers wherein it is desirable to obtain the highestdegree of undistorted amplification with a minimum number of circuitelements. However, the conventional type of coupling transformer nowemployed for this purpose is open to the limitation that a uniformamplification response characteristic can not be obtained over a Wideband of frequencies. This limitation is due to the fact that seriesresonant conditions are produced in the windings of a transformer atcertain frequencies which lie Within the operating range and whichproduce attenuation of the components of current having frequenciescorresponding to such series resonant frequencies. It has therefore beenthe practice in the past to employ resistance coupling in those circuitswherein it was desired to transmit currents having a wide band offrequencies between two electrically coupled circuits.

It is an object of my invention to provide in a high frequency circuit'atransformer which is capable of transmitting between two circuitselectric oscillations having component frequencies extending over a widerange with equalized transmission eiciency for all of the frequencycomponents within the range.

It is a further object of my invention to provide a transformer havingthe above operating characteristics which is self-contained, which issmall in size, and which is of economical construction.

In accordance with my invention, the above objects are attained bydividing the primary and secondary windings of the transformer into coilsections. These sections are designed to have different resonantfrequencies and the sections of each of the two windings are so disposedon the transformer core and so connected that a high leakage reactanceobtains between the respective coil sections.

Further, in accordance with my invention, the effects of seriesresonance between any two coil sections of either of the windings areobviated by shunting the sections having the higher resonant frequencieswith resistances having values 55 equal to the reactance values of thecoil sections which they shunt at the frequency where resonance obtainsbetween the shunted coil section and the coil section having animmediately lowei` resonant frequency.

A transformer constructed in accordance with p my invention may beconsidered as comprising a plurality of frequency transmission channels,each capable of transmitting a predetermined portion of the operatingfrequency band. The coil sections described above included in each ofthese channels are so connected and so dist posed about the core of thetransformer that the respective channels operate substantiallyindependently of each other and no undesired interaction between thedifferent channels, such as loading effects, are produced. In thismanner, all of the frequency components existing in the output from asource of `oscillations may be impressed on any form of utilizingcircuit with a uniform transmission efficiency.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organiza` tion and the method ofoperation, together with further objects and advantages thereof, willbest be understood by reference to the specification, taken inconnection with the .accompanying drawings, in which Fig. l illustratesa circuit having one form of my improved coupling unit included therein;Figs. 2 and 3 illustrate curves relating to the unit shown in Fig. 1;Fig. 4 illustrates a modification of the unit shown in Fig. 1; Fig. 5illustrates a physical embodiment of my improved transformer; Fig. 6illustrates the circuit connections for the transformer shown in Fig.Figs. '7 `to 13 inclusive illustrate the equivalent circuits of thecoupling unit shown in Fig. 5 when different frequency bands areconsidered; Fig. 14 illustrates another physical embodiment of myimproved transformer, and Fig. illustrates the circuit connections forthe transformer shown in Fig. 14.

Referring to Fig. 1 of the drawings, I have illustrated the simplestform of my improved coupling unit at I as a device for impressing theoutput from an electron discharge amplifier 2 on the input circuit of anelectron discharge amplifier 3. As shown, the coupling unit I comprisesa core 4 upon which are wound primary and secondary windings 5 and 6.The primary winding 5 is illustrated as comprising a pair of seriesconnected sections 'l and 8 and the secondary winding is comprised of apair of series connected sections 9 and I0. In order to prelil ventelectrostatic or capacity coupling between the windings 5 and B anelectrostatic shield Il is provided which is maintained at groundpotential.

In certain applications, as for example in television modulationcircuits, the oscillations which it is desired to transmit between thetwo coupled circuits may have frequency components extending over anexceedingly wide range. Thus, the discharge amplifiers .2 and 3 may forma part of an amplifying system for amplifying the signal currentsgenerated in a circuit whose energizetion is controlled in response tothe energization of a television pick-up device.

It is known that to operate satisfactorily a coupling device or couplingnetwork between two electrically coupled circuits must be capable oftransmitting between the circuits all of the frequency components of thealternating voltage impressed across terminals of the coupling systemwith a uniform transmission efficiency. Obviously, to obtain thisuniform transmission eiciency the impedance of the coupling device ornetwork must be maintained above a certain predetermined value for allof the frequency components of current flowing therein.

As will be pointed out in detail hereinafter, certain difficult problemsare involved in the construction of a transformer offering the desiredhigh impedance to currents of all frequencies within a wide range. Onesuch problem which arises in the construction of a transformer suitablefor transmitting between windings currents having a wide band offrequencies is that of eliminating undesired reductions in the impedanceof the windings produced by series resonance effects between theinductance and distributed capacity of the windings at certainfrequencies.

Such resonance effects may be overcome by dividing the primary andsecondary windings into sections having different resonant frequency,characteristics thereby to provide a plurality of channels for thetransmission of energy between the two coupled circuits. Thus thesections 3 and if! and the coupling therebetween may be considered ascomprising one channel of the coupling device of Fig. 1, and theinductively related sections l' and S may be considered as the otherchannel. By dividing the windings in this manner each of the inductivelyrelated pairs of sections may be designed to transmit a particularportion of the operating frequency range. For example, the windingsections 8 and iii may each comprise a small number of turns as comparedto the number of turns in the sections 'i and 9 respectively, and may bedesigned to have a very low distributed capacity and a higher resonantfrequency than that of the sections 'l and 9. As thus constructed, theseinductively related sections operate to transfer between the twoampliner stages the high frequency components of the oscillationsgenerated in the output circuit of the amplifier 2 and the relativelylarger sections i and 9 operate to transfer the low frequency componentsof the oscillations.

One difficulty encountered in utilizing this multi-channel method ofcoupling is that produced by resonance effects occurring between thereactances ci' the coil sections at certain Vfrequencies within theoperating frequency range. These resonance effects reduce the effectiveiinpedance of the coupling device at certain frequencies to such anextent that the transmission of currents having these frequencies may bematerially reduced or completely prevented.

The effect of resonance between the reactance of the winding sections toreduce the impedance between the terminals of the windings to currentsof certain frequencies may more clearly be understood by reference toFig. 2 wherein the impedance characteristics of the winding sections 'iand 3 of the primary Winding 5 are plotted as a function of frequency,assuming no load conditions of the transformer. In this figure, thecurves i2 and I3 represent thercalculated internal inductive reactancesof the winding sections l and 8 respectively as a function of frequencyand the curves iii and l5 illustrate the apparent external reactance ofthe same circuit elements including the effects of Vdistributed capacityof these elements. The curves I and Il show the apparent resistances ofthe windings l and 8 for the various frequencies within the operatingrange.

it will be observed that due to the distributed capacity of the coilsection l, this coil is in a resonant condition at a frequency F1 and athigher frequencies it is at first increasingly capacitively reactive andlater decreasingly capacitively reactive. This capacitive reactance issufficient at frequencies F2 (slightly higher than frequency F1) and F3to form a series resonant circuit with the inductive reactance of thesection ii. However, at the frequency F2, the apparent resistance of thesection l, as shown by curve i6, is suflicient to maintain the impedancebetween the terminals of the primary winding 5 above that predeterminedvalue below which the source of impressed voltage is overloaded. At F3,however, the apparent resistance of the winding 'i is negligible and theseries resonance produced between the reactances of the sections 'i' and8 reduces substantially to Zero the overall impedances of the primarywindings to currents of these frequencies. Hence, at this frequency, F3,and in the absence of additional means for maintaining the overallterminal impedance above the predetermined value necessary to produceequalized transmission efficiency, substantially no transfer of energyhaving this frequency will occur between the primary and secondarywindings.

In order to obviate the above diiculty and provide the necessaryimpedance in the intermediate frequency zone at which neither of thewindings 'i or 8 is otherwise effective to transmit energy, theresistance I8 is provided in shunt with the primary winding section 8.

At the frequency of resonance between the reactances of the windings land 8 the resistance i8 should be very low in order to prevent seriesresonance. However, if such a value of resistance be employed,substantially the entire effective primary section would beshort-circuited at frequencies above this series resonant i'requency.Accordingly, it has been found desirable to use a compromised value ofresistance IB, the value being determined to be equal to the inductivereacta-nce of the winding section B at the resonant frequency where thisinductive reactance is equal to the apparent capacitive reactance of thewinding section '1.

The presence of distributed capacity in and load across tlie secondarywindings 9 and lli affects the apparent reactances of the primarywindings to the extent that the resonant frequencies F1 and Fi areshifted slightly toward decreasing frequency and furthermore the peakvalues of apparent reactances and resistances may be reduced, but ingeneral the relations eX- pressed above between the values of theprimaryk that the overall impedance between the terminals of the primarywinding does not decrease below' a predetermined minimum value at anyfrequency up to the resonant frequency F4 of the winding 8. The curvefurther shows that at low frequencies the greater portion of theimpedance between the terminals of the primary winding is due -to 4theimpedance of the winding section l andat high frequencies the impedanceof the winding section 3 is predominant. At the intermediate frequencieswhere the reactance of the winding l is partially or totally in seriesresonance with the inductive reactance of the winding 8, the impedancebetween the primary winding terminals is due almost entirely to theapparent resistance of the shunt resistor i8 in parallel with winding 3.

As shown by curve I9 of Fig. 3, if the winding sections l and S beconstructed in the manner described above and the resistance i3 beprovided in shunt with the section 8, the impedance is sufficient totransmit currents having all frequencies Vless than a frequency slightlyhigher than the resonant frequency of the high frequency winding 8.

Although I have described only the effects of series resonance in theprimary winding, it will, of course, be understood that these effectsalso occur in the secondary winding and, accordingly, it is desirable toprovide resistors connected in shunt `with one secondary winding or inshunt with each of the secondary winding sections for the purpose ofpreventing series resonance effects between the winding sections fromlowering the impedance of the winding to currents having frequenciescorresponding to the frequencies at which such resonance effects occur.The value of these resistors is determined in accordance with theprinciples discussed above in connection with the primary sectionshunting resistance. Thus, in the two section secondary winding of thedevice illustrated in Fig. 1 a resistor E@ is provided having a valueequal to the inductive reactance of the winding section i@ at thefrequency where resonance obtains between this reactance and theapparent capacitive reactance of the section 9, inclusive of eiIects onthis reactance of such coupling as may exist between all windings.

The frequency range may be extended by adding additional windingsections having resonant frequencies increasingly higher than that ofthe high frequency sections 8 and il) and shunting each of thesesections with a resistance having a value equal to the inductivereactance which it shunts at the frequency of resonance of the reactanceof this winding with the reactance of the next lowerV resonant frequencywinding section.

Thus, in Fig. 4, I have illustrated a transformer constructed inaccordance with the principles outlined above in which three channelsare provided for transmitting the low, intermediate and high frequencyportions of the frequency band between the two windings. Thistransformer is illustrated as including primary winding sections 2|, 22and 23 and secondary wndingsections 2li, 25 and 26, the sections beingso designed that the inductively coupled sections 2l and 24 constitutethe low frequency transmitting channel, the sections 22 and 25constitute the intermediate frequency transmitting channel, and thesections 23 and 26 constitute the high frequency transmitting channel.Each of the higher resonant frequency sections 2-2, 2?, 25 .and .2S isshunted by a resistor having a value determined in the manner set forthabove. It will, of course, be understood that in practiceadditionalfrequency channels may be provided by increasing the number of windingsections and .providing additional shunt resistors.

In the construction of a transformer wherein all of theinductivelycoupled coil sections constituting the various frequency transmittingchannels are mounted upon the same core, it is necessary, ifsatisfactory operation is to be obtained, so to arrange the sections ofeach winding that a considerable leakage reactance is obtained betweenthe respective sections of the primary and secondary windings. Thisnecessity arises from the fact that the low capacity reactance ofcertain of the windings may constitute a heavy load on the otherwindings if the winding sections are in closely coupled inductiverelation.

In accordance with my invention, the above difficulty is obviated bymounting the winding sections on the transformer core in the mannerillustratedin Fig. and connecting the elements of the coupling unit inaccordance with the circuit shown in Fig. 6 wherein elements identicalto those of Fig. 5 are identified by like reference characters.

Referring to Fig. 5 of 'the drawings I have illustrated the transformeras comprising a core 2l upon which are mounted primary winding sectons28, 29 and 3l), and secondary winding sectionsl, 32, 33, Sli and 35. Theprimary winding section 28 and the secondary section 3l are arranged inclosely coupled inductive relation upon the center leg of the core andconstitute the Channel for transmitting currents having frequenciesextending over the low portion of the operating frequency range. Thehigh frequency transmitting channels are comprised of the primarysections 29 and til and the secondary sections 32, 33, @il and 35. Itwill be observed that the winding sections included in the highfrequency channels are mounted on the outer legs of the three-leggedcore 2l thereby to provide a high leakage reactance between thesewinding sections and the sections of the low frequency channel.

As will be more clearly brought out hereinafter the respective primarywinding sections are connected in such a manner that when the respectivewinding sections are energized the sections of the high frequencychannels including the primary winding sections 29 and 3E] aremagnetically isolated. Thus, the windings are connected in such l annerthat when the primary winding 28 is enev 'ized a ux p1 indicated by thedash lines is produced in the core which traverses the core in thedirection indicated by the arrows appended to the identified dash lines.Similarly the winding sections 29 and .30 are connected so that whenthey are energized a flux p2 is produced in the core having the directonindicated. It will be observed that the two fluxes 1 and (p2 traversethe core in such a directon that the voltage induced in the sections 29,30, 32 and 33 are opposite and, hence, the two high frequency windings29, 32 and 3U, 33 are in effect magnetically isolated from the windings28 and 3l The secondary winding sections 39 and 39 are connected so thatthe flux p1 induces equal and aiding voltages in each of these sections,while the flux (p2 induces canceling voltages. In this manner the twosections 34 and 35 are magnetically isolated from the windings formed bythe winding sections 29, 32 and 39, 33.

The Complete circuit diagram for one form of a coupling unit having atransformer such as described above embodied therein is shown in Fig. 6.In the circuit illustrated the transformer is shown as being embodied ina coupling unit for impressing the output oscillations of an electrondischarge amplifier 2 on a load illustrated as a resistance Therespective primary and secondary winding sections 28 to 35 inclusive areshown diagrammatically as being connected in a manner which will producethe desired ilux interaction as described in the preceding paragraph. Inaddition, a pair of circuits are provided for further insuring completeisolation of the respective frequency band transmission channels, One ofthese circuits comprises a condenser 36 connected in series with theprimary winding sections 29 and 39 across the primary winding section28. A resistance 31 is provided for preventing an undesired lowering ofthe operable primary winding impedance due to series resonance betweenthe winding sections 29, 39 and 58. Similarly, a resistance 49 isconnected in shunt with the sections 34 and 35 for the same purpose. Theother circuit comprises a condenser 38 connected in parallel with aresistance 39 in series with the secondary winding sections 32 and 33across the series connected secondary winding sections 3l, 34 and 35.

While the connections shown in Fig. 6, and described in detailhereafter, pertain to a transformer with multi-section windings some ofwhich are effectively paralleled, this is not to be construed as anylimitation on the theory of operation of dthe transformers described inconnection with the totally series-connected winding transformersillustrated in Figs. 1 to 4 inclusive. No structural changes in thetransformers shown in Fig. 5 and Fig'. 14 are involved thereby.

The operation of the coupling unit illustrated in Figs. 5 and 6 willbest be understood by reference to Figs. '7 to 13 inclusive wherein Ihave shown the equivalent circuits for the net work of Fig. 6, whenparticular frequency bands are considered.

For a band of frequencies extending over the lower portion of theoperating frequency range the tightly coupled primary and secondarysections 28 and 3l respectively are effective to provide a transmissionchannel for currents having frequencies within this portion of theoperating range. Over the effective transmission range of these twowinding sections the condensers 36 and 38 and the resistance 39 togetherwith the high leakage reactance between the respective primary andsecondary winding sections effectively isolate the transmitting channelscomprising the sections 519, 32 and 39, 33 and prevent these channelsfrom affecting the transmission efficiency of the channel formed by thesections 28 and 3|. For currents having frequencies eX- tending overthis low portion of the operating frequency range the impedance of thesecondary sections 34 and 35 is very low and hence the ratio of voltagetransformation is effectively determined by the turn ratio between thesections 28 and 3l.

When the range of frequencies referred to in the preceding paragraph isconsidered, the equivalent circuit for the coupling unit and tube 2'becomes as shown in Fig. '7 wherein e0 represents the voltage availablea't the input terminals of the electron discharge device multiplied bythe amplification factor of the `discharge device, p represents theinternal anode to cathode resistance of the discharge device 2', R isthe equivalent resistance formed by referring the resistance 3 to theprimary side of the transformer and X1 is the primary magnetizingreactance.

At a slightly higher band of frequencies the leakage reactance betweenthe winding sections 28 and 3l becomes appreciable as compared to R andthe equivalent circuit becomes as shown in Fig. 8. In this circuit thereactance :r2 represents the leakage reactance between the sections 28and 3l. Over this band of frequencies the primary magnetizing reactanceof the transformer becomes so large as to have a negligible effect onthe operation of the network and, accordingly, it is omitted from theequivalent circuit shown.

At a still higher band of frequencies the equivalent circuit becomes asshown in Fig. 9 wherein c1 represents the capacity of the condenser 36,c2 represents the capacitance of the condenser 38 referred to theprimary side of the transformer, the resistance R1 represents theresistance 3l, R2 represents the resistance 39 referred to the primaryside of the transformer, and the reactance x3 represents the magnetizingreactance of the winding sections 29 and 3l).k Over this band offrequencies the leakage reactance :r2 is of a magnitudeV such that thevoltage drop therethrough tends to lower the voltage across theterminals of the equivalent resistance R. However, the condensers 36 and38 become effective over this frequency band to open up the transmissionchannels 29, 32 and 39, 33 thereby to maintain the desired value ofimpressed voltage across the terminals of resistance R. It will ofcourse be understood that the turn ratio between the sections 29, 32 andthe sections 30, 33 must be the same as the turn ratio between thesections 28, 3| if the voltage across the resistance R is to bemaintained at the `desired value.

By making the reactance of condenser c1 approximately equal to .r3 inthis portion of the frequency range and further by making R1, x3, R2 andwz all equal to each other and greater than R, the network will bebroadly tuned, thereby increasing the current flowing in 9:2 and R by anamount sufficient to compensate for the voltage drop produced by theresistance R1. The resistance 31, or in Fig. 9 resistance R1, operatesto prevent series resonance, between the capacitive reactance ofcondenser 36, in Fig. 9, ci and the inductive reactance .ra at anyfrequency. Similarly the resistance 39, or in Fig. 9 resistance R2,prevents series resonance between the secondary magnetizing reactance ofthe winding sections 32 and 33 and the low frequency blocking condenser38.

At still higher frequencies the magnetizing reactance x3 of the networkshown in Fig. 9 becomes so large as to have practically no effect on theoperation of the circuit. Further, capacitive reactance of condenser C2,becomes so small with respect to the resistance R2 that the latter haslittle effect on the circuit. Thus, the equivalent circuit for a band offrequencies covering this portion of the operating frequency rangebecomes as shown in Fig. 10. Partial resonance of the network voccursover the band of frequencies which is sufficient to compensate for thevoltage drop produced by the resistor R2.

At a still higher band of frequencies the equvalent circuit for thecoupling unit illustrated in Fig. 6 may be accurately represented by thecircuit of Fig. l1 wherein R3 represents the resist- 'ance Ml of Fig. 6,:r4 represents the inductive reactance of the winding sections 3i and35, C3 represents'the equivalent distributed capacity of the windingsections 2S and 3i referred to the primary windings 29 and 3o and X5 isthe leakage reactance between primary windings 29 and 3o and secondarywindings 32 and 33. Within this band of frequencies the equivalentdistributed capacity c3 of the winding section 3l becomes of sufficientmagnitude. to constitute a considerable load across .resistance 3) whichtends to reduce the voltage available at the terinlz-ials of theresista-nce or in Fig. l'l.- R. However, at such frequencies the windingsections 34 and 35 shunted by the resistance dii maintain the overallimpedance of this branch of the equivalent circuit at a value sufficientto prevent the undesired reduction in voltage. If the circuit elementsare selected having the correct impedance values, it is possible toobtain the same voltage transfer ratio in this portion of the operatingfrequency range as is attained in the lower portions of the range.

In the arrangement of Figs. 5 and 6 it is necessary that the distributedcapacity of winding 28 be sufficiently low as not Ito constitute anobjectionable load on discharge device 2.

At the lower portion of the frequency range in which coils 34 and 35 areoperative the equivalent inductance mi of the winding sections 3d and 35is substantially equal to the equivalent capacitive reactancecorresponding to the dis-- tributed capacity of the winding section 3i.Thus, the apparent resistance R3 corresponding to the resistance lil asviewed from the input terminals of the coupling unit is the impedancewhich prevents excessive loading of the windings 32. and 33. over thisband of frequencies. It becomes. apparent from a consi-deration of thisequivalent circuit that the resistances R1 and R3 must be large ascompared to the resistance R if a uniform response characteristic is tobe obtained over a frequency range including the band at present beingconsidered.

When a still higher band of frequencies is considered the equivalentcircuit becomes as shown in Fig. 12 since the reactances represented byC3 and Cae-re now negligible and x4 extremely high.

At a still higher band of frequencies covering a range extending to theupper limit of the operating frequency range the equivalent circuitbecomes as shown in Fig. 13. In this frequency band the distributedcapacity of the winding sections 29, 3ft, 3.2 and 33 begins to have aloading effect due to the capacitive reactance thereof, which iseffectively in shunt to the resistance R. The equivalent capacityrepresenting these components of distributed capacity is represented. bythe condenser c4. At higher frequencies the loading effect of thiscondensive reactance is increasingly greater until a frequency isreached where this reactance is equal to the leakage inductivevreactance frs. 'I'his frequency represents the absolute upper frequencylimit for the operating range of the structure shown in Fig. 5 and thevoltage ratio characteristic falls off rapidly at frequencies above thisvalue.

It has been found that in certain cases the distributed capacity of thewinding 28 tends to overload the source at frequencies extending overthe upper portion of the operating range. This undesired effect may beovercome by employing the 4ransformer illustrated in Fig. 14 wherein apair ol primary winding sections M and 42 are pro vided in addition tothe elements of the transformer illustrated in Fig. 5 vthese windingsbeing connected asshown in Fig. 15. The sections 4I and i? are mountedon the outer legs of the transformer cere and are connected to bemagnetically isolated from the winding sections 29, 30, 32 and They aredesigned to have a very low distributed capacity and are shunted by aresistor 43 for preventing series resonance effects between theinductance thereofand the equivalent capacitive reactance formed by thedistributed capacity of the winding sections 28 and 3 l. This obviatesthe necessity of designing winding 28 to have low distributed capacity.

It has been found that a small coupling unit constructed in the mannerdescribed above is capable of transmitting electric circuit currentsextending over an exceedingly wide band of frequencies as for example,from 20 cycles to 100 kilocycles or even more. By employing the windingsection arrangement illustrated and connecting these sections in themanner shown, the respective frequency band transmission channels thusformed may be magnetically isolated thereby to provide a high leakagereactance between the sections included in each channel, withoutemploying a core structure of unduly large size. It will be apparent tothose skilled in the art that any number of channels may be provided byan obvious extension lof the structural arrangement and circuitconnections described in the preceding paragraphs and the band width maybe even further extended.

While I have shown a particular embodiment of my invention, it will ofcourse be understood that I do not wish to be limited thereto since manymodifications in the structure may be made, and I contemplate by theappended claims to cover all such modifications as fall within the truespirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A coupling unit for coupling together two electric circuits for thetransmission therebetween A. y

ing the inductive coupling between the primary and secondary sectionshavingV like resonant frequencies for providing a plurality of channelsfor transmitting currents having frequencies eX- tending overpredetermined portions of said frequency range.

electric circuits for the transmission therebetween of alternatingcurrents having component frequencies extending over a wide range,comprisinga transformer having a core, sectional- 70 2. A coupling unitfor coupling together two ized primary and secondary windings on saidcore, each of the sections of each of said windings having a resonantfrequency different from the resonant frequency of each of the othersections of the same winding and substantially the same as that of onesection of the other winding, the primary and secondary winding sectionshaving the same resonant frequencies being coupled in close inductiverelation thereby to provide a plurality of channels for transmittingcurrents having frequencies extending over predetermined portions ofsaid frequency range.

3. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range comprising a transformer havinga core, sectionalized primary and secondary windings on said core, eachof the sections of each of said windings having a resonant frequencydifferent from the resonant frequency of each of the other sections ofthe same winding and substantially the same as that of one section ofthe other winding, the primary and secondary sections having the sameresonant frequencies being coupled in close inductive relation therebyto provide a plurality of channels for transmitting current havingfrequencies extending over predetermined portions of said frequencyrange, and means to produce relatively large leakage reactance betweensections having different resonant frequencies whereby loading of one ofsaid channels due to the low capacity reactance of one of said sectionscorresponding to another of said channels is prevented.

4. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range comprising a transformer havinga core, sectionalized primary and secondary windings on said core, eachof the sections of each of said windings having a resonant frequencydifferent from the resonant frequency of each of the other sections ofthe same winding and substantially the same as that of one section ofthe other winding, the primary and secondary sections having the sameresonant frequencies being coupled in close inductive relation therebyto provide a plurality of channels for transmitting currents havingfrequencies extending over predetermined portions of said frequencyrange and being arranged on said core so that the leakage reactancesbetween sections having different resonant frequencies are sufficient toprevent loading of any one of said channels by the other of saidchannels, and means for preventing lseries resonance effects between therespective sections of each of said windings from lowering thetransmission efficiency of said transformer for currents havingfrequencies corresponding to the frequencies at which such resonanceeffects occur.

5. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range, comprising a transformer havinga core and including sectionalized primary and secondary windings, saidprimary and secondary windings each including a section having a lowresonant frequency and a plurality of sections having successivelyhigher resonant frequencies, said primary and secondary windingssections being coupled together in close inductive relation in the orderof their resonant frequencies thereby to provide a plurality of separatetransmission channels each effective over a predetermined portion ofsaid frequency range, and means including a resistance connected inshunt with each of said high resonant frequency sections for preventingseries resonance effects between the respective sections of each of saidwindings from lowering the transmission eiciency of said transformer forcurrents having frequencies corresponding to the frequencies at whichsuch resonance effects occur.

6. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range comprising a, transformer havinga core and including sectionalized primary and secondary windings onsaid core, said windings each including sections having differentresonant frequencies and being inductively coupled to provide aplurality of transmission channels each effective over a predeterminedportion of said frequency range, and means for preventing seriesresonance effects between the respective sections of each of saidwindings from lowering the transmission efficiency of said transformerfor currents having frequencies corresponding to the frequencies atwhich such resonance effects occur.

'7. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range comprising a transformerhaving acore, sectionalized primary and secondary windings on said core, saidwindings each including sections having respectively high and lowresonant frequencies, said high resonant frequency primary and secondarysections being inductively coupled to provide a transmission channeleffective over the upper portion of said frequency range and said lowresonant frequency primary and secondary sections being inductivelycoupled to provide a transmission channel eifective over the lowerportion of said frequency range.

8. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range, comprising a transformer havinga core, sectionalized primary and secondary windings on said core, saidwindings each including sections having respectively high and lowresonant frequencies, said high resonant frequency primary and secondarysections being coupled in close inductive relation thereby to provide atransmission channel effective over the upper portion of said frequencyrange, said low resonant frequency primary and secondary sections beingcoupled in close inductive relation thereby to provide a transmissionchannel effective over the lower portion of said frequency range, andmeans to produce relatively large leakage reactance between said highand low frequency sections whereby loading of said first-named channelby the other of said channels due to the low capacity reactance of saidlow frequency section in said upper portion of said range is prevented.

9. A coupling unit for coupling togetherY two electric circuits for thetransmission therebetween of alternating currents having componentfrespectively high and low resonant frequencies, said high resonantfrequency primary and secondary sections being inductively coupled toprovide a transmission channel effective over the upper portion of saidfrequency range, said low resonant frequency primary and secondarysections being coupled to provide a transmission channel effective overthe lower portion of said frequency range, said high and low resonantfrequency sections of each of said windings being arranged on said coreso that the leakage reactances between said sections are suiiicient toprevent loading of one of said channels by the other of said channels,and means for preventing series resonance effects between the respectivesections of each of said windings from lowering the transmissionefciency of said transformer for currents having frequenciescorresponding to the frequencies at which such resonance effects occur.

10. A coupling unit for coupling together two electric circuits fo-r thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range, comprising a transformer havinga core, sectionalized primary and secondary windings on said core, saidwindings each including sections having respectively high and lowresonant frequencies, said high resonant frequency primary and secondarysections being inductively coupled to provide a transmission channeleffective over the upper portion of said frequency range and said lowresonant frequency primary and secondary sections being coupled toprovide a transmission channel effective over the lower portion of saidfrequency range, said high and low resonant frequency windings beingconnected to form a series resonant circuit of substantially zeroimpedance at a frequency Within said range, and means includingresistances connected respectively one in shunt with each of said highresonant frequency sections and having a resistance value equal to thereactance value of the shunted section at the frequency where saidseries resonance occurs for preventing said series resonance effectsfrom lowering the transmission efficiency of said transformer forcurrents having frequencies corresponding to the frequencies at whichsuch resonance effects occur. n

1l. A coupling unit for coupling together two electric circuits for thetransmission therebetween of alternating currents having componentfrequencies extending over a wide range comprising a coregsectionalizedprimary and secondary windings on said core, said windings eachincluding sections having respectively high and low resonantfrequencies, said high resonant frequency primary and secondary sectionsbeing inductively coupled to provide a transmission channel effectiveover the upper portion of said frequency range, said low resonantfrequency primary and secondary sections belng inductively coupled toprovide a transmission channel effective over the lower portion of saidfrequency range, and means for preventing series resonance effectsbetween the respective sections of each of said windings from loweringthe transmission efficiency of said transformer for currents havingfrequencies corresponding to the frequencies at which such resonanceeffects occur.

HAROLD T. LYMAN.

